Introduction

The Tropical Atlantic Current Observations Study (TACOS) is a pilot study aimed to further the understanding of how the upper ocean circulation impacts ocean advection and mixing, sea surface temperatures (SSTs), and atmospheric processes. Ocean current velocity—both zonal (east-west) and meridional (north-south)—varies with depth and time. These fluctuations are driven by winds near the surface and density differences throughout the water column, and as a result, the current speed and direction can change.

As density changes drive currents, the moving water tends to mix with its new surroundings and change its properties. For example, diurnal to seasonal fluctuations of ocean currents strongly influence SST distributions in the tropical Atlantic. These fluctuations can be accomplished through horizontal motion (advection) and vertical motion (upwelling or downwelling).

Certain atmospheric processes are affected by surface ocean conditions. Warm sea surface temperatures provide energy for atmospheric convection, which creates thunderstorms and rain. In certain circumstances, warm sea surface temperatures can provide excess energy that strengthens the atmospheric circulation of hurricanes.

About TACOS

TACOS uses 10 acoustic current meter sensors to augment the 4°N 23°W PIRATA mooring with additional sensors between 7 and 87 m depth. Prior to TACOS, there was a lack of vertical high resolution ocean current measurements north of the equator, specifically in the Intertropical Convergence Zone (ITCZ); the ITCZ is a key region influencing tropical weather and climate.

With the implementation of TACOS, we now have prolonged observations of current and vertical shear measurements that were previously nonexistent in this location. By establishing a long-term time series of current observations at 4°N 23°W, we can better understand how ocean currents, vertical shear, advection, and mixing can modify SSTs and overlying atmospheric processes. Additionally, we can use TACOS observations to validate tropical weather models and forecasts, which presently rely on lower resolution ocean measurements. Future deployments will take place at 20°N 38°W and 12°N 38°W.

Inter-Tropical Convergence Zone

The Inter-tropical convergence zone (ITCZ) is a region near the equator, where the trade winds of the Northern and Southern Hemispheres come together. The northeast trade winds in the northern hemisphere converge with southeast winds from the Southern Hemisphere (shown below). Due to the intense solar heating near the equator, the warm, moist air is forced up into the atmosphere. As the air rises it expands and cools, releasing the moisture in a persistent series of showers and thunderstorms around the Earth’s midsection.

Seasonal shifts in the location of the ITCZ drastically affects rainfall in many equatorial regions, resulting in the wet and dry seasons of the tropics rather than the cold and warm seasons of higher latitudes.

History of the Project

PIRATA is an ongoing joint project between Brazil, France, and the United States that uses moored sensors to measure upper ocean temperature, salinity, velocity, and near-surface atmospheric parameters. By increasing the number of velocity sensors at the 4°N 23°W PIRATA Northeast Extension mooring, TACOS is helping us develop a more complete understanding of the mechanisms driving upper ocean heat advection and vertical mixing. To learn more about PIRATA you can visit NOAA’s PIRATA Northeast Extension page.

TACOS sensors were first deployed on the 4°N 23°W PIRATA Northeast Extension mooring on March 6 2017 and recovered on March 26 2018. Since the first deployment, two other deployments have occurred (2018 and 2019) and the next is being prepared for an anticipated late fall 2021 deployment at the 20°N 38°W PIRATA Northeast Extension mooring. The 20°N 38°W mooring was chosen to expand our understanding of ocean current and vertical shear fluctuations in the Atlantic main hurricane development region.